1. Field of the Invention
The present invention concerns a method for coating a mechanical member, for example to make an anti-wear coating on a tubing plate and at least on the internal terminal portion of the tubes associated therewith, so as to protect them from the corrosive action of galvanic currents, cavitation or other.
The present invention also concerns the mechanical member coated according to the method.
2. Description of Related Art
It is known to coat at least partly some types of mechanical members, such as tubing plates and at least part of the internal portion of the tubes which form the bundle of tubes, in a fluidic plant, for example a conditioning or heat exchange plant or other. The coating is normally carried out to define a protection and/or a prevention against wear which normally occurs because of operative corrosions, for example galvanic corrosions, cavitation corrosions or other.
It is known to coat such plates and such tubes with layers formed by resins or plastic compounds, having a determinate elasticity, so as to prevent the direct contact of the fluids with the tubing plate or with the tubes, at least in correspondence with the critical zones of wear.
In particular, it is known to coat the external surface of the tubing plate with a single layer of plastic material.
It is also known to coat the terminal portion of the internal surface of the tubes in an independent way from the external surface of the tubing plate with a plurality of layers of plastic material, having different thicknesses and elasticity from the layer coating the plate.
It is also known to provide that the terminal layer of the coating of the internal surface of the tubes extends so as to be disposed over the coating of the tubing plate, so as to define a substantial surface continuity between the internal surface of the tube and the external surface of the tubing plate.
This known solution determines a difference in thickness of the outermost layer of the coatings formed, such as to entail a lack of uniformity with regard to the properties of resistance to wear, between the internal portion of the tubes and the external surface of the tubing plate.
In the state of the art, the layers of coating of the internal surface of the tubes, of which the outermost layer which extends as far as the tubing plate is also a part, have a degree of elasticity which is higher than the degree of elasticity of the coating of the external surface of the tubing plate.
This further increases the dis-uniformity of the resistance to wear of known coatings and, since they have different thicknesses, there is also a different mechanical behavior of the coating between the part disposed in correspondence with the terminal portions of the tubes and the part disposed on the external surface of the plate.
Therefore this type of known solution does not guarantee an efficient and lasting protection, or prevention from erosion of the tubing plate and the tubes, and can bring about mechanical and functioning failure of the mechanical member thus coated.
Document U.S. Pat. No. 5,820,931 is known, which describes a tubing plate coated with a plurality of layers inside the tubes, one on top of the other. In this known solution, the coating layers which are radially innermost are shorter than the outermost radial layers. And so, at the end of each layer, a plurality of steps form in rapid succession with respect to each other which disturb the flow of the fluid; furthermore, this happens in a zone where the fluid enters the tubes, where vorticity, cavitation and galvanic currents are very damaging for the mechanical structure of the tubing plate.